Low‐Frequency Ocean Waves Triggered by Tropical Cyclones via Seafloor Distributed Acoustic Sensing

Propagation of low‐frequency ocean waves, including infragravity (IG) and internal waves, affect ocean dynamics and energy transfer within marine environments. IG waves are long‐period ocean surface waves that can propagate long distances across the ocean and impact the coastlines and deep ocean, while internal waves are buoyancy‐driven oscillations that propagate along density interfaces within the ocean interior. However, the influence of tropical cyclones (TCs) on the dynamics of two types of the waves across varying topographies remains poorly understood. We apply the distributed acoustic sensing (DAS) technique to a submarine cable with a water depth of 0–2,500 m deployed off Cape Muroto, Japan, and investigate the characteristics of IG and internal waves, particularly during the TC and non‐TC periods. The two waves and their frequency ranges are identified by the phase velocities estimated from the frequency‐wavenumber analysis. Our results show that the propagation directions of the two waves are altered before and after the passage of a TC (Lan), and spatial differences in their changes are also observed at different topographic regions along the cable. Moreover, we suggest that both IG and internal wave amplitudes are modulated by tidal currents, particularly near the topographic high. The observed internal waves are triggered by near‐inertial waves generated by the wind forcing during the approach of the TC Lan. This study demonstrates the effectiveness of the DAS system in monitoring low‐frequency ocean wave behaviors, with implications for improved modeling of ocean circulation by spatially dense observations.